Porch/ portico, should always be built on a foundation that extends below the frost line. Depending on which part of the country you are in will determine the depth. If you don't go below the frost line, the entire porch can heave during the freezing and thawing and slowly pull away from the house. It's best to build on proper footings, otherwise you are taking some risks of inevitable movement.

Thanks. We are in New England. It's been proposed to use 16" poured in place concrete slab by several contractors. Appreciate your thoughts.

What are the dimensions of the slab? I love the scale. Thank you

It's 4' x 8'. We could only come out 4' from the house due to front yard setback requirements by the Town.